1. Field of the Invention
The present invention relates to a spindle motor and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks about central axes thereof are typically installed in hard disk apparatuses and optical disk apparatuses. Such spindle motors include a stationary portion fixed to a housing of the apparatus and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque centered on the central axis by magnetic flux generated between the stationary and rotating portions, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary and rotating portions of the spindle motor are joined to each other through a bearing apparatus. In recent years, in particular, spindle motors have often been provided with a bearing apparatus in which a lubricating oil is arranged between the stationary and rotating portions. As an example of a bearing apparatus including the lubricating oil, US 2010/0321823 describes a bearing apparatus in which the lubricating oil is arranged between a shaft and a rotating member supported to be rotatable relative to the shaft.
In some bearing apparatuses including the lubricating oil, two surfaces, i.e., upper and lower surfaces, of the lubricating oil are defined as in the bearing apparatus described in US 2010/0321823.
In the case of such a bearing apparatus, it is desirable that the levels of both the upper and lower surfaces of the lubricating oil be measured to control the amount of the lubricating oil injected into the bearing apparatus at the time of injection of the lubricating oil. However, measuring the level of one of the upper and lower surfaces of the lubricating oil may be difficult because of the structure of the bearing apparatus. In the bearing apparatus described in US 2010/0321823, for example, a lower capillary seal portion is defined by an inner circumferential surface of a thrust cup and an outer circumferential surface of a sleeve portion of a hub, and therefore, it is impossible to check the lower surface of the lubricating oil in the lower capillary seal portion through visual inspection at the time of the injection of the lubricating oil. That is, it is impossible to measure the level of the lower surface of the lubricating oil. This makes it necessary to control the amount of the lubricating oil injected into the bearing apparatus based on only the level of the upper surface of the lubricating oil.
Moreover, in recent years, the thickness of spindle motors, in particular, has been decreasing. There has accordingly been a demand for reductions in both axial and radial dimensions of capillary seal portions. For example, a reduction in the thickness of the bearing apparatus described in US 2010/0321823 requires reductions in both the axial and radial dimensions of the capillary seal portions. This will decrease the size of a margin portion of each capillary seal portion which accommodates a variation in the level of the surface of the lubricating oil in the capillary seal portion. This leads to a possibility that a leakage of the lubricating oil out of the spindle motor will be caused by a fluctuation in the level of any surface of the lubricating oil when the spindle motor is running or by an external shocking force when the spindle motor is in a stationary state.